WO1992015143A1

WO1992015143A1 - Switching system

Info

Publication number: WO1992015143A1
Application number: PCT/GB1992/000316
Authority: WO
Inventors: Moray James Campbell; David Stewart Liddell
Original assignee: Moray James Campbell; David Stewart Liddell
Priority date: 1991-02-22
Filing date: 1992-02-21
Publication date: 1992-09-03
Also published as: GB9103757D0; AU1279792A

Abstract

The present invention relates to an automatic switching system suitable for use with a mains powered circuit supplying an electrical appliance (L1) and having a remote switching means (RS) controlling connection thereof to the mains power supply, to control an emergency power supply (BA). The system comprises an appliance status sensing means (SE) for sensing presence of mains power supply at an appliance end portion of the mains power supply cable to the appliance (L1), the remote switching means (RS) having means for bypassing at least some mains power supply to the appliance end portion of the cable when the appliance (L1) is substantially disconnected from the mains power supply by said remote switching means (RS), for deactivation of the appliance (L1). The system further includes emergency power switching means (SW) connected to said status sensing means (SE) for automatic actuation of the emergency power supply (BA), upon sensing absence of any mains power supply at the appliance end portion of the mains power supply cable.

Description

SWITCHING SYSTEM The present invention relates to an automatic switching system for controlling emergency lighting or other appliances upon failure of a mains power supply.

Fire and safety regulations and the like dictate that public building and workplaces such as hospitals, schools, nursing homes, offices and the like should be equipped with emergency lighting systems designed to be activated upon failure or accidental or otherwise disconnection of a central mains power supply. It will be understood that such emergency lighting can enhance the chances of for example persons escaping burning buildings, as well as facilitating the access of emergency services in such cases.

Conventional emergency lighting systems consist of a battery, a battery charger and an electric light mounted proximal to or integral with a standard light fitting, such that in normal use, the mains power supply powers the light fitting and charges the battery of the emergency light via the battery charger at the same time, thereby ensuring the battery is always more or less fully charges when an emergency arises. The conventional method of actuation of emergency lighting, as a result of mains power supply failure, is effected by sensing the mains power supply on the upstream side of any light switch and/or fusible link. Such sensing is achieved by running a fourth wire (in addition to the normal live, neutral and earth wires) to a light, from the power source supply cable at the upstream side of the light switch to the emergency lighting system. The emergency lighting system is provided with circuitry formed and arranged for sensing the presence or not of mains power, and switching means for actuating the emergency lighting. It will be appreciated that the installation of the fourth, sensing, wire is both costly and time consuming especially when older buildings require to have emergency lighting systems installed to complement existing electrical lighting systems.

It is an object of the present invention to avoid or minimise one or more of the above disadvantages.

The present invention provides an automatic switching system suitable for use with a mains powered circuit supplying an electrical appliance and having a remote switching means controlling connection of said appliance to the mains power supply and connected to said appliance via a mains power supply cable connecting said appliance to the mains power supply, to control an emergency power supply BA, which system comprises an appliance status sensing means formed and arrange for sensing, directly or indirectly, presence of mains power supply at an appliance end portion of said mains power supply cable in use of the system, said remote switching means being formed and arranged for passing at least some mains power supply through said mains power supply cable to said appliance end portion thereof both when the appliance is connected to and disconnected from the mains power supply by said remote switching means said system further including emergency power switching means connected to said status sensing means and formed and arranged for automatic actuation of said emergency power supply in use of the system, upon sensing absence of any mains power supply at said appliance end portion of said mains power supply cable whereby in use of the device said emergency power supply is automatically activated upon loss of mains power supply in said mains power supply cable remote from said appliance end portion. The present invention also provides an automatic switching system suitable for use in controlling an emergency power supply to an electrical appliance having a remote switching means controlling connection of said appliance to the mains power supply and connected to said appliance via a mains power supply cable connecting said appliance to the mains power supply, which system comprises an appliance status sensing means formed and arranged for sensing, directly or indirectly, presence of mains power supply at an appliance end portion of said mains power supply cable in use of the system, said remote switching means being formed and arranged for passing at least some mains power supply through said mains power supply cable to said appliance end portion thereof both when the appliance is connected to and disconnected from the mains power supply by said remote switching means, said system further including emergency power switching means connected to said status sensing means and formed and arranged for automatic actuation of said emergency power supply, in use of the system, upon sensing absence of any mains power supply at said appliance end portion of said mains power supply cable whereby in use of the device said emergency power supply is automatically activated upon loss of mains power supply in said mains power supply cable remote from said appliance end portion.

Thus with an automatic light switching system of the present invention, emergency lighting sys^tems may be readily installed in a simple and economic manner without the need for extensive rewiring between the power source supply on the upsteam side of a remote, for instance wall mounted, switch and the light.

For the avoidance of doubt it will be understood that the terms appliance as used herein extends to lighting installations, multiple or single, and may also include any other electrically operated apparatus such as, for example, incubators, air conditioning systems or the like where interruption of operation can give rise to particular problems. Furthermore it will be understood that said appliance end portion of said mains power supply cable includes that portion of said cable connected to said appliance and any portion of said cable more or less closely proximal the appliance connected thereto.

Preferably the remote switching means comprises an in-line switch provided with a bypass signal transmission means formed and arranged for passing an electrical signal from the mains power supply side of said in-line switch to the appliance side thereof at the remote switching end portion of the mains supply cable for transmission along said mains supply cable.

In one possible form of such a remote switching means the by-pass signal transmission means simply comprises trickle current and/or voltage transmission means, e.g. a high impedance conducting pathway, for passing a small fraction of the full mains supply around the in-line switch.

In another form of such a remote switching means the signal transmission means may comprise a pulse and/or tone signal generator, directly or indirectly, connected to both said sides of the lin-line switch and formed and arranged for generating a characteristic pulsed and/or tone signal indicating presence of a mains power supply at the mains power supply side of the in-line switch and transmitting it along said mains power supply cable to said appliance end portion thereof. In another preferred form of the invention the remote switching means comprises a signal transmitter having an actuation means and formed and arranged for transmitting control signals to a local switch means provided at said appliance end portion of the mains power supply cable downstream of said appliance status sensing means, for connecting and disconnecting the appliance from the mains power supply, said mains power supply cable passing said remote switching means substantially uninterrupted.

Various appliance power supply status sensing means may be used in accordance with the present invention depending on inter alia the particular form of remote switching means used. In general where either full or partial (trickle) mains power supply is delivered to the appliance end portion of the mains power supply cable then there may be used a more or less simple current or voltage detector.

Where a pulsed or tone signal transmission is used from the remote switching means to signal the presence (or absence) of mains power supply thereat, then the sensing means would comprise a suitable decoder.

Thus in one form of the present invention using a simple trickle current by-pass means, conveniently in the form of an impedor in parallel with the in-line switch, so long as there is a mains power supply to the remote switching means and said switch is open, a trickle current, preferably not exceeding 10mA, for example 1mA, will be supplied to the appliance and may be sensed thereat. If the said remote switching means is closed then of course the full mains supply will be supplied to the appliance and may be sensed thereat. When the sensing means senses no power supply at all to be present, the emergency power supply is activated by said switching means. A particularly preferred form of by-pass means comprises a suitable capacitor, generally a so-called X- or Y- rated capacitor, which passes a small current less than that required to maintain the existing light unit on when that is switched off from an "on" condition. The particular current level required to maintain a fluorescent lighting unit on will depend on the tube and its driving circuit. In general though there is used a capacitor which limits the.current passed to a value in the range from 2 to 20mA.

In another form of the invention using a signal transmitter this may be in the form of a pulse encoder and the sensing means includes a pulse decoder or there could be used an audio oscillator and PLL/LP filter (phase lock loop/low pass) , respectively. Desirably said signals may be coded for individual detection and said detectors may be formed and arranged for receiving only predetermined signals whereby a plurality of detectors in use in a multiple lamp lighting system may be selectively controlled by a central transmitter for the switching on and/or off of individual lamp units each having a respective detector.

The emergency power supply will usually be in the form of a low voltage battery powered system and it will generally be desirable for this to be coupled to the mains powered appliance in such a way as to avoid any direct current path therebetween. Conveniently such electrical isolation is achieved with an opto-isolator or the like so as to permit the appliance, to operate under normal conditions at the supply voltage (e.g. 240V.A.C.) and the emergency power supply to operate at low DC voltage such as are readily obtainable from battery supplies. In the case of lighting appliances in particular it will be appreciated that the emergency or back-up power supply may be used either to supply the appliance which is being backed up or to drive a 5 separate back-up lighting appliance.

It will be appreciated that the sensing means may be disposed at either side of the electrically isolating coupling between the mains powered supply and the emergency power supply system. Most conveniently though 10 the sensing means is incorporated in the latter.

The emergency power switching means is preferably directly associated with the emergency power supply and conveniently uses comparator means to compare a reference signal with the output signal of the sensing 15 means. Conveniently the emergency power switching means includes relays, or other suitable means such as diode switches, solid-state relays, and other devices.

Preferably the emergency power supply includes a mains supply transformer or main voltage dropper circuit for

20 driving a battery charger used to maintain a rechargeable battery in a substantially fully charged state. Preferably said battery is charged by said battery charger more or less all the time, irrespective of the remote switch position. In the case of an

25 emergency lighting system the emergency power supply is connected, in use, to a suitable lighting appliance e.g. a fluorescent light. Conveniently said emergency power supply may be mounted in direct proximity to or inside the housing of an existing light unit.

30 It will be understood that various different arrangements may be used to provide emergency lighting using a switching system of the present invention. Thus for example the battery may be used, in the event of a mains failure, to power the existing lighting unit ordinarily powered directly by the mains supply, with the aid of a suitable converter between the battery and the existing lighting unit. In another form of the invention the battery may be used to power an auxiliary lighting unit, to replace the existing lighting unit in the event of mains failure. Naturally the invention can also be used to switch on a lighting unit in the event of mains failure, in mains circuits other than lighting circuits to provide an indication of loss of mains supply to other types of appliance e.g. machinery or office equipment. Further details of such applications are provided hereinbelow with reference to the preferred embodiments described.

It will be appreciated that as the installation of the system of the present invention avoids the need for additional wiring extending between an appliance and its remote switching means, installation may be readily effected with minimal disruption to the fabric of the building or other structure in which it is being installed. Moreover the ease and simplicity of installation minimizes the down-time in the premises concerned which can be a significant advantage in commerical situations such as factories and theatres. Furthermore with preferred forms of the invention, charging of the rechargable batteries of the emergency power supply is maintained continuously even when the appliance is switched off. This can be particularly advantageous in the case of appliances which are used relatively infrequently.

Further preferred features and advantages of the present invention will appear from the following detailed description given by way of example of some preferred embodiments illustrated with reference to the accompanying drwings in which:-

Fig. 1 is a block circuit diagram of an automatic switching system according to a first embodiment of the invention;

Fig. 2 is a detailed circuit diagram of an automatic switching system suitable for use in the embodiment of

Fig. 1;

Fig. 3 is a detailed circuit diagram of a second embodiment of an automatic switching system of the invention; and

Figs. 4 to 6 are detailed circuit diagrams of third to fifth embodiments of the invention.

Fig. 1 shows a schematic block circuit diagram of an automatic switching system of the invention generally indicated by reference number 1. The system 1 comprises a remote switch Rs on the live side L of a 230v A.C. mains supply Su. The mains supply Su powers a battery charger Ch for charging a battery Ba, and a switch over unit Sw switches between the supply Su and the battery

Ba. The switch over unit Sw is controlled by an emergency sensor unit Se. An emergency supply converter

Co is formed and arranged for supplying power to a light

Li in an appropriate A.C. or D.C. form.

The remote switch RS comprises an in-line manually operable switch 2 in parallel with a trickle bypass element 3. In use and with the switch 2 in a closed position, the supply Su will supply the light Li in the normal way and also supply the battery charger Ch for charging the battery Ba. If the switch 2 of the remote switch RS is opened the sensor unit Se will detect only a tricle mains supply through the trickle bypass element 3 and will maintain the switch over unit Sw in its normal position. In this way switch 2 controls the mains powered appliance turning it on and off while maintaining throughout, the supply to the battery charger Ch.

When the sensor unit Se detects no "signal" (whether this be simply the presence of a trickle current or a more complex signal) by any suitable means including comparing the received signal with a predetermined signal (See Fig. 2) corresponding to a complete absence of power available from the mains supply Su it causes the switch over unit Sw to isolate the light from the mains supply circuit and connect the battery supply Ba to the light I&.

A detailed circuit suitable for use in the embodiment of Fig. 1 is shown in Fig. 2 in which like parts corresponding to those in Fig. 1 are identified by like reference indicia.

Fig. 3 is another detailed circuit suitable for use in a second embodiment of the invention wherein the remote switch RS comprises a momentary connection switch 2 for momentarily operating a encoder En to send a coded signal tone down the mains supply cable. A decoder De senses and decodes the tone and switches a local switch at the light end of the mains power supply cable, which local switch is in the form of a relay shown in broken line as R in.-Fig. 1 and RBi in Fig. 3, to an ON or OFF condition from a previous OFF or ON condition, thereby to connect or disconnect the light L>ι to or from the mains power supply.

It will be understood the mains supply is normally available to the local light switch relay RB^ and battery charger Ch at all times. When mains supply is lost the switchover switch Sw automatically isolates the light Li from the mains supply (irrespective of the condition of RBi) and connects it to the emergency supply Co.

Fig. 4 is another detailed circuit suitable for use in a third embodiment of the invention which is somewhat similar to the embodiment of Fig. 3, wherein the remote switch RS is in the form of an in-line ON/ON or momentary disconnection switch 2 formed and arranged for momentarily breaking the mains power supply Su to a monostable 4 sensor unit Se which in turn causes a flip-flop 5 to change the condition of the local switch R thereby switching the light L^ to an ON or OFF condition from a previous OFF or ON condition.

It will be appreciated that various other forms of switching, sensing, remote switching and controlling of a switching system may be employed such as for example microprocessor control.

The circuits of Figs. 5 and 6 are generally similar to those previously described apart from the following differences. In the embodiments of Figs. 5 and 6 the trickle by-pass unit at the remote switch RS is in the form of a mains or X- rated capacitor SCI which has a value such that it passes only a small current below that required to maintain the discharge in the existing fluorescent light L^ which is generally around 20mA per fluorescent light unit LI. The capacitor SCI also has connected in series therewith surge stopping resistors SRI and SR2 which have low resistance, and in parallel, a resistor SR3 having a high resistance in order to allow discharge of said capacitor.

In these embodiments a bridge rectifier BR is used in the charging circuit Ch and is also connected to the mains supply through a mains or X- rated capacitor Cl to provide a trickle current to the charger, and eventually the battery Ba. When the remote switch RS is on providing full mains supply to the existing light Li, the charging circuit has a current of the order of 5OmA, and when the remote switch RS is off, this is reduced to some 20mA but is still sufficient for recharging or at least sustaining the battery Ba.

The sensing means SE in these embodiments simply comprises a PNP transistor TR1 connected downstream of the bridge rectifier BR so that it is retained in an OFF condition via bias resistors R4, R5 connected to its base, so long as a DC current supply from the bridge rectifier (corresponding to the presence of a mains supply at the remote switch RS) is maintained. This in turn keeps a relay RA deactivated. When the mains supply fails so that no charging current is supplied, the transistor TR1 base is grounded via resistor R5 and a capacitor C3 connected in parallel with the transistor TRl and relay RA discharges therethrough to ground thus operating the change-over relay RA which switches on the battery Ba from charging mode to discharge or operating mode. The battery Ba now latches "on" the relay via diodes D4, D2 and resistor R7. The latter resistor reduces the "hold-on" current through relay RA, to a minimal level so that when the battery voltage falls to a predetermined level the relay RA will revert to its deactivated condition thereby isolating the battery Ba from its load by means of the blocking diodes D3 and D4.

The emergency supply convertor Co in this case is in the form of an HT oscillator circuit which produces a high frequency, high voltage output which is capable of directly striking and maintaining a separate fluorescent tube emergency light LE as in the embodiment of Fig. 5 without any ballast or glow starter being needed. In the embodiment of Fig. 6 which is of the maintained change-over emergency light type, there is used a four-pole change-over relay RA/4 which is formed and arranged so as to isolate an existing light unit L^ from the mains supply and connect it to the convertor CO output whilst also isolating the latter from the starter of said existing light unit L^.

The embodiments of Figs. 5 and 6 are particularly preferred in view of inter alia their relatively simple, economic and compact form of construction thereby facilitating ready integration of the system within the lighting units and drop-down switches of exzisting installations with the minimum of disruption.

As described above, the emergency power supply means is conveniently in the form of a battery especially a rechargeable battery and for the avoidance od doubt the present invention includes within its scope switching systems with such emergency power supply means, irrespective of whether such batteries are supplied installed in battery mounting and coupling means of the system, or are supplied separately.

Claims

CLAIMS 1. An automatic switching system suitable for use with a mains powered circuit supplying an electrical appliance (LI) and having a remote switching means (RS) controlling connection of said appliance to the mains power supply and connected to said appliance (LI) via a mains power supply cable connecting said appliance (LI) to the mains power supply, to control an emergency power supply BA, which system comprises an appliance status sensing means (SE) formed and arrange for sensing, directly or indirectly, presence of mains power supply at an appliance end portion of said mains power supply cable in use of the system, said remote switching means (RS) being formed and arranged for passing at least some mains power supply through said mains power supply cable to said appliance end portion thereof both when the appliance (LI) is connected to and disconnected from the mains power supply by said remote switching means (RS) , said system further including emergency power switching means (SW) connected to said status sensing means (SE) and formed and arranged for automatic actuation of said emergency power supply (BA) , in use of the system, upon sensing absence of any mains power supply at said appliance end portion of said mains power supply cable whereby in use of the device said emergency power supply (BA) is automatically activated upon loss of mains power supply in said mains power supply cable remote from said appliance end portion.

2. A switching system as claimed in claim 1 wherein said remote switching means is provided with a trickle current by-pass means (3).

3. A switching system as claimed in claim 2 wherein said trickle current by-pass means comprises a mains rated capacitor means (SCI) .

4. A switching system as claimed in claim 3 wherein said capacitor means (SCI) is formed and arranged for passing only a small current less than that required to maintain operation of a gas discharge lighting unit appliance (LI) .

5. A switching system as claimed in any one of claims l to 4 when in combination with a said emergency prior supply (BA) in the form of a rechargeable battery connected to a charging means (CH) connected to the appliance end portion of the mains power supply cable.

6. A switching system as claimed in claim 5 wherein the sensing means (SE) is connected to the output of said charging means (CH)

7. A switching system as claimed in claim 6 wherein said sensing means (SE) comprises a transistor means

(TR1) formed and arranged so as to be held in an "off" condition by means of bias resistor means (R4, R5) connected to its base.

8. A switching system as claimed in any one of claims 5 to 7 wherein is provided a switching means (SW) formed and arranged for disconnecting the battery (BA) from said charging means (CH) upon actuation of the emergency power switching means (SW) in response to sensing of absence of any mains power supply at said appliance end portion of said mains power supply cable.

9. A switching system as claimed in any one of claims 5 to 8 wherein the emergency power supply means includes a converter means (CO) formed and arranged) for producing a high frequency high voltage output.

10. A switching system as claimed in any one of claims 1 to 8 wherein said emergency power switching means (SW RA/2/4, RA/4/4 is formed and arranged for connecting, in use of the system, said emergency power supply (BA) to a said electrical appliance (LI) , mains supply powering of which is ordinarily controlled by said remote switching means (RS) .

11. A switching system as claimed in claim 10 wherein is provided a switching means (SW, RA/2/4, RA4/4) formed and arranged for isolating said electrical appliance (LI) from the mains power supply cable upon connection of said appliance (LI) to the emergency power supply

(BA)-

12. A switching means as claimed in any one of claims 1 to 8 wherein said emergency power switching means (SW) is formed and arranged for connecting, in use of the system, said emergency power supply (BA) to an emergency electrical appliance (LE) .